Mineral Technology Series No. 17 



Bulletin No. JfS 


University of Arizona 
Bulletin 


Gems and Precious Stones 
of Arizona 

BY 

FRANK L. CULIN, JR. 



Entered as second class matter Novem¬ 
ber 23, 1915, at the postoffice at Tucson, 
Arizona, under the Act of August 24. 
1912. Issued weekly, September to May. 


PUBLISHED BY THE 

University of Arizona 
COu-v a. * &T Bureau of Mines 

n 

Charles F. Willis, Director 
TUCSON, ARIZONA 


1916-17 




BIBLIOGRAPHY 


Bauer, Max. Precious stone; translated by L. J. Spencer, illustrat¬ 
ed with colored plates; C. Griffin & Co., London, J. B. 
Lippincott, Agents, Philadelphia. ($15.00). 

Claremont, Leopold. The gem cutter’s craft; George Bell and 
Sons, London, 1906. ($5). 

Crookes, Sir William. Diamonds; Harper & Brothers, London and 
New York, 1909. (75 cents). 

Farrington, O. C. Gems and gem minerals; illustrated with col¬ 
ored plates. A. W. Mumford Co., Chicago, 1903. ($3). 

Kunz, G. F. Gems and precious stones of North America; illus¬ 
trated with colored plates; Scientific Publishing Co., New 
York, 1890. ($10.00). 

Min. Bureau No. 37, San Francisco, 1905. 

History of Gems Found in North Carolina; Bull. N. C. 
Geol. Survey No. 12. 

Rothschild, M. D. Handbook of precious stones; G. P. Putnam’s 
Sons, New York, 1890. ($1). 

Smith, F. G. H. Gem stones; illustrated with colored plates; Me¬ 
thuen & Co., Ltd., London, 1912. ($2.10). 

Streeter, E. W. Precious stones and gems; illustrated with colored 
plates; George Bell and Sons, London, 1898. ($4). 

Tassin, Wirt. Catalogue of gems in the United States National 
Museum; Ann. Rept. U. S. Nat. Mus. 1900. 

Williams, G. F. The diamond mines of South Africa; 2 vols., 
illustrated with colored plates; B. F. Buck & Co., New 
York, 1905. ($25). 


0 . o* 

JAN 30 1917 




3 



\S% 

University of Arizona Bulletin 


Mineral Technology Series No. 17 February 6, 1917 


GEMS AND PRECIOUS STONES OF ARIZONA 
By Frank L. Culin, Jr. 

INTRODUCTION 

Nearly all the known varieties of gems and precious stones are 
found in the United States, and several varieties are found in Arizona. 
Little systematic mining has been carried on for them, and no exten¬ 
sive search for them has been made, except in the states of Maine 
and North Carolina. In most cases, the discovery of gems in the 
United States has been accidental in connection with other substances 
that are being mined, or in small veins. 

These gems are mostly sold in local markets; gem collectors and 
mineralogists also purchase them, for private collections, as a rule. 

ARIZONA GEMS 

The best known gems found in Arizona are the turquoise, garnet, 
peridot, chrysocolla, azyr-malachite, malachite, agate, chalcedony, 
amethystine quartz, diamond (meteoric) dioptose and topaz. 

Turquoise: Turquoise is a phosphate of alumina and copper. As 
a rule, it has greenish or light milky blue color; also it is commonly 
a dark blue, which fades on exposure. These varieties are hardly 
worth the cost of cutting. The gem stone should be a clear dark 
blue, which will not fade. When veined or mottled with the gangue 
matrix the substance is known as matrix turquoise. This matrix is 
usually as hard as, and even harder than, the turquoise itself. The 
color of the matrix should be pleasing, and harmonize with the blue 
of the turquoise. 

Turquoise occurs as veins or vugs in acid igneous rocks. It seems 
to have been formed by deposition from warm waters, and is usually 
associated with altered rocks. 

Garnet: Garnet is a complex silicate of calcium and aluminum, in 
which the calcium is frequently replaced by more or less iron and 
magnesium, and the aluminum, by chromium and iron. It varies in 
color from white to black-red, yellow, green and brown shades. The 
best quality garnets are dark red, free from specks and cracks or 






,2 


Arizona State Bureau of Mines 


other flaws. This variety is called pyropene garnet. When of a 
purplish tint, it is known as almandine. The brown variety is in¬ 
correctly called hyacinthe. 

The precious garnet found in Arizona is known as the Arizona 
Ruby, although it is not at all related to the true ruby; it is as 
fine as any found in the world. They are gathered as worn, rounded 
pebbles, in gravel deposits in the northern part of the state, mostly by 
the Moqui Indians. The gem has not been found in place in this 
state, but was probably formed in basic rocks, such as peridotite. It 
also occurs in mica schist rocks in other localities, and may be found 
in such rocks in this state. 

Peridot: Peridot is a clear pure crystalline variety of the mineral 
chrysolite or olivine, a magnesium-iron silicate. The best quality 
stones have a clear yellow-green tinge. It is usually brown or olive 
green (olivine) and rarely a clear golden yellow (chrysolite). The 
material from Arizona comes from altered peridotites, in the north¬ 
ern part of the state, near Ralkai and Rice. It is usuallly found in 
sands and gravels. Large good stones are hard to find. The stone 
is increasing in popularity. 

Chrysocolla: Chrysocolla is a hydrous silicate of copper. It is 
not of much value as a gem stone unless it has been silicified. It is 
of a light blue color, usually, or it may be more or less mottled. It 
is found in many copper mines of the state, being very abundant in 
the Globe district. 

Azurite and Malachite : Azurite and malachite are hydrous silic¬ 
ates of copper. Azurite is the blue carbonate, and malachite green. 
The two minerals are nearly always very closely associated, and the 
combination is known as azure-malachite. Malachite is most valu¬ 
able when it shows rounded or oval workings and a silky lustre. 
These minerals are common in the copper mines of Arizona. 

Agate: Agate is a variegated chalcedony which is a variety of 
quartz. The variegations usually take the form of bands, which, 
when parallel and of alternating colors, form onyx and sardonyx. 
When these variegations take the form of moss-like or dendritic 
growths, the mineral is called moss agate. It is usually formed by 
successive deposition in cavities in eruptive rocks. They are found 
in many places in the state; in place in lavas, in sands and gravels, 
and embedded in limestones. 

Chalcedony: Chalcedony is quite common in Arizona, usually 


Mineral Technology Series No. IJ 


3 


of a bluish gray or buff color. The red variety, carnelian, and the 
green variety, chrysoprase, have not been found in Arizona. It is 
formed in rock cavities, and found in place or in sands and gravels. 
A variety of chalcedony known as “turtle-back” or moonstone has 
been found here. It shows a peculiar mottled appearance, when cut, 
resembling the back of a turtle. Chalcedony is often called moon¬ 
stone when cut, but improperly so. 

Amethystine Quartz'. Amethystine quartz is a clear purple col¬ 
ored quartz. The best known occurrence is in the McConnico dis¬ 
trict. According to the Mineral Resources of the United States 
for 1908, one crystal from this district was sold to Tiffany, of New 
York City, for $59.00. The great objection to it as a gem is 
that it loses color. It is found in veins and vugs, often with silver 
and lead ores. 

Diamond: The only diamonds found in Arizona are meteoric, 
and occur in meteoric iron found at Canyon Diablo, near Coon 
mountain, in the northern part of the state. The crystals are very 
small, and have no commercial value. 

At one time, in 1870, a company was organized for the explora¬ 
tion of diamonds and other gems in Arizona and New Mexico. 
A great quantity of gems said to have been found in these fields was 
exhibited, and expeditions to the locality gathered approximately 
6000 carats of rubies and 1000 carats of diamonds. 

Topaz: Topaz is a fluo-silicate of aluminum, usually clear and 
colorless, but most valuable when golden yellow or blue in color. 
It is found in the northern part of Arizona. The golden yellow var¬ 
iety is very apt to fade. 

METHODS OF EXTRACTION AND PREPARATION. 

Most of the gems and precious stones found in Arizona are merely 
by-products of the mining of other substances, and are sorted out 
from poorer specimens. The turquoise, garnet and peridot are mined 
separately. There are several companies that have produced tur¬ 
quoise in Arizona. The garnets are gathered from the sand and 
gravel beds in which they are most commonly found. 

In preparing precious stones for market, the best specimens are 
first selected, cleaned, cut in various shapes, and polished. Poorer 
specimens are also cut and polished, or they may be reserved for use 
in private and public collections. 


4 


Arizona State Bureau of Mines 


THE GEM INDUSTRY. 

There was a large decline in the gem industry in 1914, due to 
the restricted conditions imposed by the conflict in Europe. This 
decrease had not been expected, but nevertheless, almost all gems 
fell off in production; turquoise, however, showed an increase. 

The total value of the gem production of 1914 was $124,651. The 
following table shows the total value of the production of gems 
which, although found in Arizona, may or may not be produced in 


the state. 

Agate ..$ 8,312 

Amethystine quartz . 255 

Azurite. 1,280 

Chalcedony (Included with agate) 

Chrysocolla (Included with azurite) 

Dioptase (Included with azurite) 

Garnet . 1,760 

Malachite (Included with azurite) 

Peridot. 100 

Topaz . 1,380 

Turquoise . 13,370 


Total .$26,457 


(Note. It is to be understood that this does not represent the 
Arizona production. No figures as to that are available.) 

The value of the imports of precious stones into the United 
States in 1914 was $19,211,084, showing a decrease of $26*220,914 
from 1913. 


ESSENTIAL PROPERTIES OF GEMS. 

Gems are certain minerals which, by reason of their brilliancy, 
hardness and rarity, are valued for personal decoration; the term is 
extended to include pearl. _ (Definition from Encyclopedia Brit- 
tanica). In a restricted sense the term is applied only to precious 
stones after they have been cut and polished as jewels, while in their 
raw state, the minerals are conveniently called gem stones. 

The general properties which determine the value of a gem are: 

(1) hardness; (2) specific gravity; (3) crystalline form and 
cleavage; (4) color; (5) optical properties, refraction and dispersion, 
pery’on. 

(1) Hardness—A high degree of hardness is a desirable property 
of a gem, for no matter how brilliant and beautiful a mineral may 











Mineral Technology Series No. 17 


5 


be, it is less valuable to the jeweler if it is not sufficiently hard to 
withstand the abrasion to which articles of personal use are sub¬ 
jected. (This statement does not apply to pearls and a few other 
gems.) If not sufficiently hard, the stone may be badly scratched; 
it will at least soon become dull by wear. An arbitrary scale of 
hardness has been adopted, with the diamond, the hardest known 
gem, placed at the top with a value of 10. The ruby and sapphire 
come next, with a value of 9; the topaz is placed at 8, and quartz at 7. 

(2) Specific gravity: This property in itself does not directly 
affect the value of a gem stone, but it is very valuable in distinguish¬ 
ing one stone from another. 

(3) Crystalline form and cleavage:: The majority of gem 
stones are crystalline in character. They lose their original crystal¬ 
line form in cutting, but due to the crystalline structure, most gem 
stones have definite cleavagee planes. This property is usually taken 
advantage of in dressing stones preparatory to cutting. 

(4) Color: The beauty and consequent value of gems depend 

mainly on their color. Some stones, of course, as the diamond, re 

valued for absence of color, but this is the exception. Color is 

usually due to the presence of some foreign pigmentary matter, 

usually in small proportions. The coloring matter may be evenly 
distributed throughout the stone, or in regular zones, or in quite 
irregular patches. 

(5) Optical properties: Refraction. The brilliancy of a cut 
stone depends on the amount of light reflected from its faces; in 
the form known as the “brilliant”, the gem is so cut that much of 
the incident light, after entering the stone and suffering refraction, 
is totally reflected from the facets at the back. The amount of 
light which is thus returned to the eye of the observer will be 
greater as the angle of total reflection, or critical angle, is smaller, 
but this angle will be small if the refractive power of the stone is 
great; so that the brilliancy depends directly on the refractivity. 

Dispersion: The play of colors exhibited by a cut stone, often 
known as its “fire”, is due to the decomposition of the white light 
which enters the stone, and is returned, by internal reflection, after 
resolution into its colored components. 


VALUE OF GEMS 

Wholesale Prices: 

Turquoise is worth up to $100 a pound at the mine, in the rough, 
but usually is less valuable. Matrix material brings from $5 to $25 
per pound. Cut matrix turquoise costs from 10 cents to $10 a 


6 


Arizona State Bureau of Mines 


carat. Cut clear blue turquoise costs from $1 to $10 a carat, the 
price increasing with size. When cut in large quantities, stones may 
be cut for three to five cents a carat. 

Garnet is sold in the rough as single stones, and brings a price 
rather less than one fifth the price of cut stones. Cut pyropene gar¬ 
nets are worth from 50 cents to $2 a carat, depending on the quality. 
Almandine garnets, if resembling the emerald, cost $12 to $15 a 
carat. The cost of cutting is $1 to $1.50 per carat. 

Peridot is also sold as separate stones. Cut material runs from 
$2 to $15 a carat. $5 usually buys a good stone. Cutting costs 
from $1 to $1.50 a carat. 

Copper bearing stones, excluding high grade malachite, sell for 
about $10 a pound. When cut, they are sold by the stone rather 
than by carat, and are sold so as to make a profit! No definite price 
can be set. They cost from five cents to ten cents a carat for cutting. 

Chalcedony, unless of the turtle back variety, is hardly worth $1 
per pound. Cut material is barely Worth the cost of cutting, which 
is 5 to 10 cents a carat. Turtle back variety may bring $5 or more 
for a stone. 

Amethystine quartz is almost valueless, except as mineral speci- 
mentsm unless it holds its color. The cut American material is 
hardly worth more than the cost of cutting. But foreign material 
may be worth $4 a carat when cut. The cost of cutting is from 
50 cents to $1 a carat. 

Topaz is bought by the single stone. Fine gem crystals, when 
colored, may be worth $50 to $100. Cut material, in dark blue 
shades, brings $10 to $25 a carat; the fine golden yellow brings $4 a 
carat; diamond cut white stones bring $1 to $2 a carat. The cost 
cutting is about $1 a carat. 

ECONOMIC CONSIDERATIONS 

With the exception of a very few valuable and highly prized stones, 
the production of gems is almost always more or less spasmodic. 
The cause of this is usually over production during a period of de¬ 
mand. This over production is often purposeful—as an example, 
the tourmaline mines of San Diego County, California, produce a 
large supply, which provides for the market demands for a time, 
and when this supply runs low, the mines are again operated until 
the stock is replenished. 

In figuring upon a deposit of gems or precious stones, usual pre¬ 
cautions must be taken. The product must, of course, be of good 
quality. The demand for the material should be known and a 


Mineral Technology Series No. 1 7 


7 


market arranged for. The question of transportation does not 
enter, to any great extent, since the bulk is not large, and the 
quantity .small. 


FUTURE OF THE INDUSTRY 

There is no question but that there will always be a large demand 
for gems. Aside from a few varieties, as the diamond, ruby, pearl, 
sapphire, etc., the demand is quite variable, but is always sufficient 
to repay small efforts in the production of various stones. 

In Arizona the turquoise and garnet are sure of a wide market, 
at almost all times. Gems of the copper group, azurite, malachite, 
dioptase, etc., will find a market, not always steady, but fairly so, 
especially with curio seekers. 

Although there is, as has been seen, quite a wide variety of gems 
and precious stones in Arizona, one could hardly say that prospects 
of any great or continued production are good. What production 
there is will probably always be on a small scale. 


































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